It is sometimes necessary to supply power to a load located in a hazardous environment. For example, electric solenoid controlled valves are sometimes located in paint spray booths for controlling the supply of paint and air to an automatic spray gun. When the paint is atomized during spraying, highly volatile, flammable paint solvents may be present in the spray booth. If the power supply wires connected to a valve actuating solenoid should become either open circuited or short circuited, there is a risk of a spark causing a fire or an explosion in the spray booth. In a conventional power supply for operating paint valve solenoids, a zener barrier circuit consisting of zener diodes and resistors may be used to limit the amount of energy available for ignition within the spray booth. The amount of current available to the load is limited by the series resistance of the zener barrier circuit and the characteristic input impedance of the load device. When the load becomes detached, the available voltage is clamped by the zener diodes to a level above the normal operating voltage for the load, but the current is only limited by the series resistance of the zener barrier circuit. The available current may be much higher than the normal operating current of the load.